Stringed instruments such as the guitar and violin operate by tensioning a string between two points at opposite ends of the instrument known as the nut and the bridge. The string is suspended and tensioned between the nut and bridge and is plucked or otherwise vibrated to establish a standing wave which produces the sound perceived by the listener. The nut and bridge define terminal nodes of the standing wave and establish the wavelength of the standing wave defined by the vibration of the string. The frequency of the note produced by the string is, in part, a function of the distance between the string's terminal nodes. Commonly, stringed instruments include a fingerboard situated in longitudinal proximity to the strings, allowing the musician to press the string in contact with the fingerboard at a point between the nut and the bridge. The point of contact with the fingerboard establishes a new or substitute terminal node between the bridge and the nut at the point of contact, (referred to as a "stop") thereby changing the wavelength and frequency of the string's vibration in compliance with the effective length of the string between the bridge and the stop. Ordinarily, the nut defines a terminal node only when the string is sounded in the open position, i.e., without an intermediate stop established on the fingerboard. The bridge almost always defines a terminal node, wherever the string is stopped. Some instruments, like the violin, have fingerboards which are smooth and allow the musician to stop the string at any point on the fingerboard and thus produce an indefinite number of notes corresponding to an indefinite number of possible effective string lengths or "stop positions." Fingerboards of other instruments, like the guitar, have frets to establish predetermined stop positions for defining a finite series of predetermined effective string lengths and corresponding notes which the string may produce.
Conventional frets are made from wire which is cut into lengths corresponding to the width of the fingerboard and are usually partially inlaid into the fingerboard. The portion of the fret which protrudes from the fingerboard, at its uppermost point or apex, comes in contact with the string when the musician presses the string toward the fingerboard and thus determines the location of the stop on the string. The design of a well tempered instrument requires that the stop positions be at precise locations on the string in relation to the nut and bridge, referred to as "fret positions", which are spaced from one another by fret intervals. Fret intervals shorten as they ascend the neck toward the bridge of the instrument. Ideally, frets are designed and installed so that the stop positions coincide with fret positions on the strings.
The use of conventional frets adds significantly to the cost of manufacturing and maintaining a fretted instrument because there are typically more than a dozen such frets on the fingerboard of the instrument and their installation is a time-consuming process. In addition, when the instrument is used, the frets tend to wear at the point of contact with the string, causing the apex of the fret to become a flattened surface. Such wear may be the result of various techniques used by musicians to produce notes having frequencies corresponding to string lengths which do not coincide with fret positions. One such technique is to press the string into contact with the closest point of the fingerboard until the string is in contact with a fret and then to slide the string across the fret, thereby increasing the tension on the string and raising the frequency of the note produced. Alternatively, the musician may stretch the string before bringing it in contact with the fret and then sliding it on the fret back into a neutral position, known as "pull-on". In addition to causing wear, the sliding contact of the string on the fret often produces unwanted noise.
As a fret wears down, the stop position drifts from the fret position toward the nut, putting the instrument out of tune. Worn frets can be replaced, but the replacement process is costly and it damages the fingerboard of the instrument to such an extent that after several repairs the fingerboard or entire neck of the instrument must be replaced. Lately, these problems have been exacerbated because of the preference for the sound produced by bigger frets, referred to as the jumbo and super jumbo frets. These frets provide a superior physical impedance at the stops and provide the instrument with a greater sustain and preferred pull-on sound, but because of their bulk, they allow the stop position on the string as a result of wear to drift even further from the bridge than do conventional frets.
It is common for a musician to slide his fingers along a string in moving contact with the fret board to produce a sliding variation of the frequency produced by the string. Conventional frets give this sliding technique a choppy sound and irritate the musician's fingers.
One attempt to provide an improved fingerboard has been seen in which portions of the fingerboard between fret positions are inclined, giving the fingerboard a sawtooth longitudinal cross-section with the short jags of the sawtooth disposed toward the bridge of the instrument. The apex of each sawtooth acted as a stop when the musician pressed the string toward the fingerboard at a point below the apex. In addition, this sawtooth fingerboard allowed the musician to slide his finger on the fingerboard toward the bridge in a smooth motion. However, the point of contact of the fingerboard with the string was the sharp edge of the apex of the sawtooth and the high pressure at the point of contact resulted in severe wear along that edge. The wear resulted in a shifting of the stop position toward the nut, similar to the effect of wear in a conventional fret. Further, the musician could only slide his fingers comfortably on the fingerboard toward the bridge, since the short jags caught the fingers when the musician tried to slide toward the nut. This sawtooth fingerboard was not a commercial success and it is believed that it is no longer available to the public.